The present invention relates to a radio transmission apparatus and a radio transmission method for transmitting various information by a radio signal, for example, between a plurality of communication terminals.
As a conventional method of retransmission control in radio transmission, a method has been used which starts a timer after transmitting information, and retransmits the information whose receipt acknowledging information has not been transmitted from an information receiver before time-out of the timer.
Also, consideration has recently been given to a method which packetizes information to be transmitted by an information transmitter into predetermined size and transmits resulting packets by radio, and reconstructs the original information by collecting the packets at an information receiver.
The method has been considered for use in conjunction with a selective retransmission type automatic retransmission control method (SR-ARQ system), which transmits information that the information receiver has successfully received a packet to the information transmitter as receipt acknowledging information, and selects and retransmits only an unreceived packet from the information transmitter.
In addition, as a conventional method of packet transmission, a retransmission method capable of dealing with a burst error in a transmission line has been realized which, in retransmission control, waits for a reply of receipt acknowledging information from the information receiver over a certain long period of time, and then retransmits a packet whose receipt acknowledging information has not been received.
Furthermore, as a conventional technique, a method has been proposed which prevents unlimited retransmissions of packets by setting a finite number of retransmissions.
By setting such a limit on the number of retransmissions, it is possible to use the same sequence number repeatedly, and thus make efficient transmission.
Furthermore, when using the conventional selective retransmission type automatic retransmission control method, by returning a certain amount of receipt acknowledging information in one transmission, it is possible to reduce packets, which represent the number of pieces of information flowing in a radio transmission line, and thus reduce information traffic.
Such conventional retransmission control methods need to start a timer every time information is transmitted. Therefore, when information is packetized for transmission, a timer needs to be started for each packet.
Also, with a method of retransmission after waiting for a certain long period of time, when a time for retransmission is to be controlled by software, it is difficult for the software to determine that an access right on a transmission line has been obtained. Therefore, there occurs a time difference between a time when a timer is started and a time when a packet is actually transmitted, and thus the time when a timer is started cannot be used for precise retransmission control.
In addition, the conventional retransmission method using a timer needs to handle a time of a retransmitted packet. Therefore, a timer needs to be started for each packet so as to handle its time.
Moreover, in addition to control of a time for retransmission, it is necessary to handle a time for discarding a packet whose receipt acknowledging information has not been received after repeated retransmissions.
Furthermore, when using the conventional selective retransmission type automatic retransmission control method and returning a certain amount of receipt acknowledging information in one transmission, it is necessary to define a time for integrating the receipt acknowledging information. This reduces a degree of freedom in designing transmission apparatus, and makes it impossible to secure compatibility between apparatus of different manufacturers.
Furthermore, even if the time for integrating the receipt acknowledging information is defined, the receipt acknowledging information cannot be returned unless an access control right is obtained. Therefore, a time required obtaining the access control right needs to be set as a redundant time, and thus the time for integrating the receipt acknowledging information needs to be reduced in effect.